The present invention relates generally to variable resonant circuits and more particularly to an electrically variable filter circuit. In an exemplary embodiment the electrically tuned filter is employed in a radio frequency transmitting device.
The commercial availability of voltage variable capacitors has given rise to a number of electrically tuned resonant circuits. Thus, for example, electrically variable filters have been employed in intermediate frequency stages of radio receivers. Channel selecting employing electrically varied capacitors has also been accomplished in television receivers.
One drawback of such electrically tuned resonant circuits is that such circuits have a relatively limited range of resonant frequencies due to the limitations on the range of reactance change achievable by the voltage variable capacitor.
The present invention is particularly beneficial in an exemplary specific embodiment of a marine single-sideband transceiver. Such transceivers typically employ plug-in filter strips for each channel which are individually aligned for the appropriate channel. This approach requires considerable space in the radio and many extra components. It is also difficult to align, since often the capacitor value must be selected by trying various fixed values until the proper reponse is obtained.